This application is based upon and claims the benefit of Japanese Patent Applications No. 11-118563 filed on Apr. 26, 1999, and No. 2000-45143 filed on Feb. 17, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates generally to a pressure sensor having a sensor element portion for detecting pressure and a pressure conduction portion for conducting pressure to the sensor element portion, and a method for assembling the same.
2. Description of the Related Art
FIG. 11 shows a conventional pressure sensor, which can be used as a fuel pressure sensor for detecting pressure in, for instance, a vehicle fuel tank (detected body). A silicon-made sensor chip J1 is bonded to a glass-made base J2 to form a sensor element portion J3 for detecting pressure. The sensor element portion J3 is fixedly accommodated in a recess of a housing J4 molded with polybutylene terephthalate (PBT) or the like.
The housing J4 is formed with a pressure conduction portion J6 defining a conduction passage J5 therein for conducting pressure toward the sensor element portion J3. An O-shaped annular groove J7 is formed on the outer circumference surface of the pressure conduction portion J6, and O-shaped ring J8 is retained in the groove J7. The pressure conduction portion J6 is connectable, by insertion, to a member of the detected body such as a hose communicating with the fuel tank. The O-shaped ring J8 seals the connected portion.
Generally, in this kind of pressure sensor, after the sensor element portion J3 is attached to the housing J4 holding the O-shaped ring J8, sensor pressure characteristics and the like are checked. After that, the pressure sensor is assembled with a member (detected member), a pressure of which is to be detected, at the pressure conduction portion J6 through the O-shaped ring J8.
Thus, the pressure sensor is assembled with the detected member after several check steps are performed in the state in which the O-shaped ring J8 is attached to the pressure conduction portion J6. In this case, as shown in FIG. 11, a rubber-made cap J9 is attached to the pressure conduction portion J6 until immediately before the pressure sensor is connected to the detected member. The cap J9 covers the O-shaped ring fixation portion (sealed portion) to thereby prevent foreign matter from sticking to the O-shaped ring fixation portion during the manufacture process.
In the method for protecting the O-shaped ring fixation portion by the cap J9, however, the pressure characteristic check is performed after the cap J9 is attached to the pressure conduction portion J6. Therefore, the cap J9 must be detached for a while for the check in which a check jig is connected to the pressure conduction portion J6 so that check pressure is conducted into the sensor element portion J3 through the conduction passage J5.
The attachment and detachment of the cap J9 during the manufacture process increases time and deteriorates workability. In addition, foreign matter may stick to the fixation portion when the cap J9 is detached. The foreign matter sticking to the fixation portion causes leakage of pressure, sealing deficiency and the like when the pressure sensor is assembled with the detected member. These problems occur not only when the pressure conduction portion is sealed by the O-shaped ring but also when it is sealed by a packing member, screw fastening or the like.
The present invention has been made in view of the above problems. An object of the present invention is to prevent foreign matters from sticking to a sealed portion of a pressure sensor where the pressure sensor is sealed to a detected member, until immediately before the pressure sensor is attached to the detected member.
According to a first aspect of the present invention, a method for assembling a pressure sensor includes preparing a pressure sensor having a sensor element portion for detecting a pressure and a pressure conduction portion defining therein a conduction passage for conducting the pressure to the sensor element portion. The method further includes attaching a protection member having an opening portion to the pressure conduction portion so that the conduction passage communicates with an outside of the pressure sensor through the opening portion.
Accordingly, a sealed portion of the pressure conduction portion where the pressure conduction portion is to be sealed to a detected member is covered until immediately before the pressure sensor is connected to the detected member to detect the pressure. Foreign matter is prevented from sticking to the sealed portion until immediately before the pressure sensor is connected to the detected member.
Because the conduction passage communicates with the outside thereof through the opening portion of the protective member, a check pressure can be conducted toward the sensor element portion through the opening portion of the protective member and the conduction passage to check sensor characteristics of the sensor element portion in the state where the sealed portion is covered with the protective member.
According to a second aspect of the present invention, a pressure sensor includes a sensor element portion, a pressure conduction portion, and a protective member detachably attached to the pressure conduction portion to cover a sealed portion of the pressure conduction portion. The pressure conduction portion has an opening portion through which a conduction passage in the pressure conduction portion communicates with an outside thereof.
Accordingly, sensor characteristics can be checked without detaching the protective member from the pressure conduction portion. As a result, foreign matter is not stuck to the sealed portion during the check.